you realise that this thread started back in October last year when Sonar X3 was released.
As for Sonar X.
Cakewalk started off as the name of the Software sold by Twelve Tone systems in the late 80's/Early Nineties.
It ended with Cakewalk Pro Audio 9.
The next version adopted the name Sonar in about 2000/1, which was then followed By Sonar 2 etc right up to Sonar 8 then Sonar 8.5. there was no Sonar 9. It was at that point that development cycles became longer than the usual annual upgrade. At that time also Cakewalk adopted a new styling and GUI convention that they dubbed Skylight which has been the characteristic look of the X series.
In 2010/11 Sonar X series began and it was made clear to us that X did not stand for the Roman numeral for 10 rather just the letter X. So in its roughly annual release Cycle, that saw X1 and X2 take 3 years to develop, last year in October 2013 we saw the release of Sonar X3. Whether Cakewalk adopt the annual upgrade cycle again we don't know but if that were the case a new version would not be due until about October 2014.